1. Field of the Invention
This invention is a novel method for perfusion of a porous implant which achieves efficient interpenetration of desired factors into the pores or channels of the implant, cleaning of the implant, efficient passivation of the implant (inactivation of pathogens, microorganisms, cells, viruses and the like and reduction in antigenicity thereof), and the novel implant produced by such treatment.
2. Description of Known Procedures For Implant Treatment
As used in this disclosure, the term xe2x80x9cimplantxe2x80x9d refers to any material the implantation of which into a human or an animal is considered to be beneficial. Accordingly, the implant may be tissue-derived material, such as bone, skin, and the like, or it may be a metallic or synthetic material having an internal structure that may require cleaning or sterilization. Bearing this definition in mind, it will be apparent that many procedures have been described in the art for treatment of implants to either clean such implant, inactivate contaminating microorganisms or cells that may be present in or on such implant, or to infuse the implant with desirable factors. This section of the disclosure discusses several known methods for achieving one or more of these results, in order to more clearly and definitively set forth that which has been invented, and which is disclosed and claimed as novel and inventive, as defined by the claims appended hereto.
European Patent Application No. EP 0 424 159 (Osteotech)xe2x80x94xe2x80x9cAseptic Processing of Allograft Bone and Tissue,xe2x80x9d (published Apr. 24, 1991, based on a U.S. Priority application filed Oct. 9, 1989), is an extremely general disclosure relating to aseptic processing of allograft bone and issue. It appears that the intent of this application was to establish an early priority date in an effort to foreclose the entire field of aseptic processing of allograft bone and tissue. However, he disclosure is so general that it does not appear to contain an enabling disclosure of any protectible allograft sterilization method. No U.S. or European patent related to this extremely general published application appears to have ever issued.
In U.S. Pat. No. 5,333,626 (Cryolife)xe2x80x94xe2x80x9cPreparation of Bone for Transplantationxe2x80x9d, (issued on Aug. 2, 1994, based on an application filed on Dec. 31, 1991), relates to a method of preparing bone for transplantation by maintaining the internal matrix of the bone to be implanted, preferably at high pressure, in the presence of a decontaminating agent, preferably polyvinyl pyrrolidine-iodine (PVP-I) optionally in the presence of a detergent, in solution. The xe2x80x9chigh pressurexe2x80x9d feature of this patent is described at column 5, lines 10xe2x80x9431: xe2x80x9cHigh pressure washing conditions should provide a force sufficient to drive the cleaning solution into internal matrix of the bone. Such high pressure washing conditions include, for example, vigorous agitation, such as with a paint can shaker, or high pressure lavage such as with a high pressure liquid jet stream . . . The pressure of the liquid jet stream is preferably 100 to 3,000 psi and most preferably 500 to 1,500 psi.xe2x80x9d However, the patent does not disclose or suggest exposure of an implant to an oscillating atmospheric pressure, the referenced patent requires pressures significantly higher than those required according to the present invention, and it is only applicable to bone, while the present invention is applicable to bone or soft tissue. In addition, the claimed process requires approximately 1-2 days to complete.
In U.S. Pat. No. 5,513,662 (Osteotech)xe2x80x94xe2x80x9cPreparation of Bone for Transplantationxe2x80x9d (this patent issued on May 7, 1996 as a continuation-in-part of the application that issued as the U.S. Pat. No. 5,333,626 patent, based on an application filed on Jan. 21, 1994, and claiming priority to the Dec. 31, 1991 filing date of the application on which the U.S. Pat. No. 5,333,626 patent is based), relates to a method of preparing bone for transplantation in which the internal matrix of the bone is maintained at a pressure below one atmosphere. It is disclosed (column 10, lines 13-19) that xe2x80x9coptimum times for maintaining pressure below ambient are generally in the range of 30 to 60 minutes but can be determined for each application by monitoring progress of blood and lipid extraction (see Example 10).xe2x80x9d It is further disclosed that generally use of gas pressure below ambient for less than two minutes will be ineffective and use for longer than five hours will confer no further benefit. Thus, the ""662 patent requires that the bone be maintained for substantial periods of time at pressures below one atmosphere. There is no disclosure or suggestion of rapidly cycling between elevated and decreased pressures, even though it is suggested that the bone might first be treated at an elevated pressure, followed by a treatment step at a pressure below atmospheric pressure (see, for example, claim 3, column 15). The present invention discloses a process wherein transient and cyclical exposure of an implant material to a given pressure achieves the desired result of implant cleaning, perfusion or passivation.
In U.S. Pat. No. 5,556,379 (LifeNet Research Foundation)xe2x80x94xe2x80x9cProcess for Cleaning Large Bone Grafts and Bone Grafts Produced Thereby,xe2x80x9d (issued on Sep. 17, 1996 based on an application filed on Feb. 27, 1995, and claiming priority of an earlier, abandoned application, filed Aug. 19, 1994), describes the xe2x80x9cAllowash(trademark)xe2x80x9d process. The patent is explicitly directed to the removal of xe2x80x9cbone marrow from the luminal and cancellous bone spaces in large, essentially whole, bone grafts.xe2x80x9d (See Summary of the Invention). Accordingly, the referenced patent is directed only to treatment of bone, which has to be largely intact. The stated intent in applying the process to essentially whole bone grafts is to reduce the load of potentially virus carrying bone marrow to facilitate preparation of smaller bone grafts therefrom. The process involves applying a vacuum to the bone graft to draw solution capable of solubilizing bone marrow through articulating cartilaginous surfaces and through the intact bone""s intramedullary canal or other bone cavity. The patent neither discloses nor suggests a method in which oscillating pressures are used to clean a bone graft.
U.S. Pat. No. 5,380,826 (Aphios Corporation)xe2x80x94xe2x80x9cSupercritical Fluid Disruption of and Extraction from Microbial Cells, (issued on Jan. 10, 1995, based on an application filed on Sep. 29, 1992), relates to a method for harvesting intracellular components by exposing cells to an elevated pressure in the presence of a solvent, and then rapidly and suddenly releasing the pressure to effect disruption of the cells. The patent also discloses an apparatus for carrying out this process continuously. However, this patent neither discloses nor suggests applying the cell disruption method to allograft bone.
U.S. Pat. No. 5,288,462 (Stephen D. Carter)xe2x80x94xe2x80x9cSterilization Apparatus and Methodxe2x80x9d (issued on Feb. 22, 1994, based on an application filed on May 18, 1992), describes a chamber for receiving a material to be sterilized by repeatedly subjecting the chamber to elevated pressures, followed by sudden release of the pressure, i.e. xe2x80x9cexplosive decompression.xe2x80x9d The patent requires that the chamber be pressurized to at least 1000 psi. The patent neither discloses, suggests, nor claims application of this method or chamber to sterilization of bone materials. There is no disclosure of cleaning solutions used in connection with the described apparatus that would be effective in sterilizing the matrix of a bone. There is no disclosure that would allow one skilled in the art to determine, without undue experimentation, that bone could be sterilized in this apparatus. In addition, there is no disclosure nor suggestion that an implant could be sterilized without use of such highly elevated pressures, but merely by oscillation of lower absolute pressures.
U.S. Pat. No. 5,725,579 (Bioland)xe2x80x94xe2x80x9cProcess for Treating Bone Tissue and corresponding Implantable Biomaterialsxe2x80x9d, (issued Mar. 10, 1998, based on a priority French application filed Dec. 21, 1992 and an earlier U.S. priority filing of Dec. 9, 1993), is directed to a method of cleaning bone by exposing the bone to a supercritical fluid. As best as can be understood from this patent, this involves exposing bone to carbon dioxide at elevated pressures, in order to solubilize lipids.
Tissue sterilization methods known in the art have undesirable attributes. Gamma irradiation, in order to ensure destruction of pathogens, such as the human immunodeficiency virus (HIV), has to be used at doses that result in tissue destruction (e.g. 3.5 Mrad; see, for example, Rasmussen, et al., J. Arthroscopic and Related Surgery, 10(2):188-197, (1994); Goertzen, et al., British Soc. of Bone and Joint Surg., 77:204-211 (1005); Loty, et al., International Orthopaedics, 14:237-242, (1990)). Use of ethylene oxide has been found to result in implants that produce inflammatory responses (Kudryk, et al., J. Biomedical Materials, 26:1477-1488, (1992); Thoren, et al., Clin. Orthopaedics, 318:259-263, (1995); Simonian, et al., Clin. Orthopaedics, 302:290-296, (1994); Jackson, et al., Am. J. Sports Medicine, 18:1-9, (1990)). Standard chemical solution treatments, while effective in sterilizing surfaces with which the solutions are brought into contact, have the major disadvantage of being insufficiently penetrating to reach the interstices of tissues, where potentially pathogenic organisms may reside. In view of these shortcomings, there remains a long-felt-need for an optimized tissue sterilization process, which would incorporate some or all of the following features: Effective removal or inactivation of a wide range of bacterial and viral pathogens; absence of graft toxicity; retention of desirable tissue characteristics, such as biomechanical strength or growth-inducing properties; effectiveness across a wide range of operating modifications and for a wide variety of tissue types; ability to conclude the process in a final implant tissue container, to ensure sterile packaging and delivery for implantation.
In view of the foregoing review of the known art relating to implant treatment and sterilization methods, it is believed that the present invention provides a long needed improvement in that no absolute temperatures or pressures are required to achieve efficient implant cleaning, perfusion, or passivation. In addition, the instant method does not require drilling of holes in implant materials or any other manipulation or modification in order to achieve efficient implant cleaning and sterilization. Furthermore, the present method permits safe pooling of donor tissue for implant production at economies of scale, without at the same time diminishing the desirable biological properties of the pooled implant materials. The instant process includes a number of methodologies, the additive effect of which is the production of highly cleansed, sterilized (passivated) tissues, which may be implanted, without causing toxicity to the recipient. Various embodiments of the method of this invention includes all of the above listed features, namely: effective removal or inactivation of a wide range of bacterial and viral pathogens; absence of graft toxicity; retention of desirable tissue characteristics, such as biomechanical strength or growth-inducing properties; effectiveness across a wide range of operating modifications and for a wide variety of tissue types; ability to conclude the process in a final implant tissue container, to ensure sterile packaging and delivery for implantation.
This invention provides a process wherein an oscillation of pressure is created in a chamber containing an implant material in the presence of various cleaning solutions (0.5% tri( n-butyl)phosphate, TNBP; hydrogen peroxide and the like). The process essentially comprises the following steps, assuming a metallic or synthetic material having an internal matrix or space, or manually cleaned (debrided) graft material, which may or may not have undergone initial machining, is used as the starting material:
1. Rapidly evacuate the chamber containing the implant, autograft, allograft or xenograft material;
2. Rapidly backfill the chamber with cleaning solutionsxe2x80x94e.g. H2O2/Triton X-100/TNBP/Betadine mixtures;
3. Pressurize chamber;
4. Rapidly cycle between steps (1) and (3), for between about 1-150 cycles, maintaining a temperature of between about 35-40 degrees centigrade, with optional application of ultrasonic energy;
5. Machine the product as desired if not previously machined;
6. Repeat steps (1)-(4) using the same or a different cleaning compositions, optionally under elevated or reduced temperature; and
7. Optionally perform a surface decontamination step, preferably in the final packaging, as in exposure to vapor phase H2O2 or like surface decontamination treatments known in the art.
The absolute pressures of the system do not appear to be extremely critical to achieving deep, penetrating cleaning of the implant or graft materials. Rather, it is the rate of pressure cycling, the fact of cycling, and possibly the amplitude of pressure cycling, that appears to be critical to the success of this method. Accordingly, the entire process may be successfully conducted at pressures above or below one atmosphere. Evacuation pressures of 25 inches of mercury to the vapor pressure of the solutions in the chamber are adequate. Backfill pressures of between about 40 and 100 PSI are also adequate. Preferably, the entire process is conducted in a chamber which permits for sonication of the contents throughout or at particular stages of the process. In addition, preferably, the entire process is conducted in a programmable system under computer or programmable logic circuit control, so that manual processing is minimized and reproducibility of the process is maximized. Where the processed tissue is a bone implant or any form of allograft or xenograft tissue, election of appropriate solvents, such as urea (preferably about 6 M), or other chaotropic reagents, (e.g. 4 M guanidine hydrochloride, or the like), has the additional advantage of producing a processed tissue of even lower antigenicity than if such treatment were not included. Target decontamination goals for this process include:
Between about a one (1) to twelve (12) log reduction in bacterial contamination
Between about a one (1) to fifteen (15) log reduction in enveloped virus contamination
Up to about a five (5) log reduction in non-enveloped virus contamination
Between about a two (2) to ten (10) fold reduction in endotoxin
Maintenance of implant or graft biologic and biomechanical properties
absence of tissue toxicity due to cleaning solutions used
reduced implant antigenicity
Accordingly, it is an object of this invention to provide a method for production of safe and effective allograft, autograft, xenograft, metallic or synthetic implants in an efficient, economical manner.
It is a further object of this invention to permit safe pooling of tissue donor sources for implant production, while minimizing the risk that any single contaminated donor will contaminate any other donor tissue or any recipients of the pooled tissue processed according to the method of this invention.
Another object of this invention is to provide a method for cleaning, perfusing or passivating implant materials without at the same time compromising the desirable biological properties of the starting implant materials.
A further object of this invention is to produce implant materials of reduced antigenicity.
Further objects and advantages of this invention will become apparent from a review of the complete disclosure, including the claims which follow.